It's not hard to think of plausible political motives - the Pilgrims' search for religious freedom is more sympathetic than a commercial venture based on the labor of slaves and indentured servants, especially for political liberals. But in point of fact, do American schoolchildren learn about the Pilgrims because some person or institution with large influence over American education acted on some motive like this?
There are few absolutes in American education but one fairly consistent truth is that what happens in classrooms across the country is never the result of one individual person. The system of public education in America is simply too big and too unwieldy for change to happen at the curriculum level as a result of one person's actions. Instead, there are a number of factors that led to the ubiquity of Plymouth and a limited focus on Jamestown including schools' interest in localized history and a construct referred to as Americana. I've answered similar questions before so I'll be cribbing a bit from some of them.
First, due to courts and policymakers' interpretation of the US Consitution, education is a matter left up to the states. While there is a Secretary of Education and a federal Education Department (more on that history here), the decisions related to what students learn are primarily up to the states. (The exception to this is the big picture idea of math, reading/English Language Arts, and science - that is, the 2001 law No Child Left Behind required states to develop math, reading/ELA, and science standards and assess student performance in the subjects in grades 3-8 and at the high school level. But even then, it was up to the individual states to decide the specifics. We have to save Common Core for 2030, alas.) The lack of a national system of the curriculum has a whole bunch of consequences (negative and positive) but it's likely the most profound impact is in history education.
What this means practically speaking is that while students in Montana or North Dakota have historically gotten limited instruction in the history of Jamestown, students in Virginia (and likely surrounding states) have always learned about the colony multiple times. Students in Texas learn about the Alamo while students in New York State spend more time on the war of 1812 than students in Arizona. Learning about missions has long been part of the California history curriculum, etc. etc. At the same time, there are also regional differences - students in western New York State spend more time on the Erie Canal than do students in and around NYC. (I go into more detail about the history of history class in different states here.) To a certain extent, this is tied to the idea of school field trips and the idea of discovery learning or "object teaching" that was becoming increasingly common beginning in the progressive movement in the early 1900s. However, such localized instruction could be seen in classrooms during the common school era as making connections to local events, groups, and places as a popular way to engage children in content.
The reason, however, why the "history" of Pilgrims and Plymouth Bay are taught in all 50 states is about one of the purposes of public education. (The quotes around history are mostly because what's taught is less about the historical record and more about something else. American schoolchildren have long been able to pick a Pilgrim out of a lineup while having no idea who the Wampanoag people are.)
This great post from u/anthropology_nerd explores the role of Thanksgiving and the Pilgrims in the story of America and we see the push for a national origin myth in the way Thanksgiving has historically been taught in American schools. The simplified history of a struggling, brave group of settlers getting help from a gentle, neighboring group of native people helps reinforce the idea of American exceptionalism. There is an entire collection of such simplified history including Geroge Washington and his cherry tree (and not his lifelong obsession with recapturing a young Black woman who emancipated herself from his household), Christopher Columbus "discovering" a place where millions of people already lived, and the pledge to the flag. All of these simplified histories developed in service to schools as a place where children are taught an American identity as defined by the white educators who have shaped the look and nature of the American curriculum since the rise of the common schools in the 1820s.
While there is more to be said, I remember u/anthropology_nerd had a great write up over at https://www.reddit.com/r/AskHistorians/comments/cn3j2l/why_are_plymouth_rock_and_the_mayflower_such/?utm_source=share&utm_medium=ios_app&utm_name=iossmf